Turbocharger

ABSTRACT

The invention relates to a turbocharger ( 1 ) in which the bearing-housing-side diffuser wall is thermally decoupled in order to reduce the heat introduction at the bearing housing cover ( 5 ). The turbocharger ( 1 ) comprises a turbine ( 2 ), a compressor ( 3 ) which has a diffuser, and a bearing housing ( 4 ) which is arranged between the turbine ( 2 ) and the compressor ( 3 ) and which has the bearing housing cover ( 5 ). Said bearing housing cover ( 5 ) is composed of a material with a low thermal conductivity of at most 5 W/mK, for example a temperature-resistant plastic.

The invention relates to a turbocharger according to the preamble ofclaim 1.

A generic turbocharger is known from EP 1 256 703 B1.

Turbochargers of said type are used in internal combustion engines inorder to increase the engine characteristic values such as power andtorque and to reduce exhaust-gas emissions and specific fuelconsumption. At low circumferential speeds of the compressor wheel, atemperature increase of the compressor flow occurs at thebearing-housing-side housing wall of the diffuser. Since the bearinghousing constitutes the connecting element between the turbine and thecompressor, considerable internal heat transfer takes place from theturbine side to the compressor side. In the present prior art, thetemperature increase arises in that while thermally highly conductivemetallic materials are used, the relatively low flow speeds generate anincreased residence time of the fluid in the diffuser.

It is therefore an object of the present invention to provide aturbocharger for an internal combustion engine according to the preambleof claim 1, which turbocharger reduces the introduction of heat from thebearing housing into the diffuser in order to reduce the introduction ofheat from the diffuser into the compressor flow and to thereby increasethe compressor efficiency at low circumferential speeds.

Said object is achieved by means of the features of claim 1.

Subclaims 2 to 6 relate to advantageous refinements of the invention.

In a particularly preferred embodiment of the turbocharger, therefore,it is provided that a radial enlargement of the bearing housing coveralso covers the region of the diffuser wall of the bearing housing. Areduction in the introduction of heat can be obtained in this way. Toreduce the introduction of heat, the bearing housing cover is, inrelation to the prior art, produced from a material with a considerablylower thermal conductivity of less than 5 W/mK and in particular of lessthan 1 W/mK, such as for example a temperature-resistant plastic. Inthis way, the thermal conductivity of the bearing housing cover can bereduced at least by a factor of 20 in relation to metallic materials.

Further details, advantages and features of the present invention willemerge from the following description of exemplary embodiments on thebasis of the appended drawings, in which:

FIG. 1 shows a schematically highly simplified, cut-away illustration ofan exhaust-gas turbocharger;

FIG. 2 shows a sectional illustration of the modified bearing housingand of the modified bearing housing cover composed of plastic.

FIG. 1 shows a schematically highly simplified illustration of aturbocharger 1 which comprises a compressor 2 and a turbine 3. Theturbocharger 1 self-evidently has all the other conventional components,the description of which is however not required for the explanation ofthe principles according to the invention and which has accordingly beenomitted.

FIG. 2 illustrates an enlarged sectional view of a bearing housing 4 ofthe turbocharger 1, which bearing housing 4 is arranged between theturbine 2 and the compressor 3 and has a bearing housing cover 5. Saidbearing housing cover 5 is composed of a material with low thermalconductivity, for example a temperature-resistant plastic, whose thermalconductivity is less than 5 W/mK. As can be seen from said figure, thebearing housing cover 5 has been enlarged to such an extent that it canalso cover the region of the diffuser wall (not illustrated in FIG. 2)of the compressor 2.

To obtain a further reduction in the heat flow from the bearing housing4 to the bearing housing cover 5, a cavity 6 is provided between thebearing housing cover 5 and the bearing housing 4. Said cavity 6 isarranged in an outer cover region 7 as viewed in the radial direction Rof the bearing housing cover 5. The air in said cavity 6 has a thermalconductivity which, at a maximum, is lower than that of the plastic ofthe bearing housing cover 5 by a factor of 200, and said air therebyforms a further insulating layer between the bearing housing 4 andbearing housing cover 5.

The bearing housing cover 5 may also have a metal bush 10 in the regionof a cover bore 9 which holds piston rings 8, in order to preventincreased wear of the non-metallic bearing housing cover at the point ofcontact with the piston rings 8.

To complement the above written disclosure, reference is made explicitlyto the diagrammatic illustration in FIGS. 1 and 2 of the invention.

LIST OF REFERENCE NUMERALS

1 Turbocharger

2 Turbine

3 Compressor

4 Bearing housing

5 Bearing housing cover

6 Cavity

7 Cover region

8 Piston rings

9 Cover bore

10 Metal bush

1. A turbocharger (1) having a turbine (2), having a compressor (3)which has a diffuser, having a bearing housing (4) which is arrangedbetween the turbine (2) and the compressor (3) and which has a bearinghousing cover (5), wherein the bearing housing cover (5) is formed froma material with a thermal conductivity of less than 5 W/mK.
 2. Theturbocharger (1) as claimed in claim 1, wherein the bearing housingcover (5) is composed of a temperature-resistant plastic.
 3. Theturbocharger (1) as claimed in claim 2, wherein the thermal conductivityof the bearing housing cover (5) is at most 1 W/mK.
 4. The turbocharger(1) as claimed in claim 1, wherein the bearing housing cover (5) coversa diffuser wall of the compressor (3).
 5. The turbocharger (1) asclaimed in claim 1, wherein a cavity (6) is provided between the bearinghousing cover (5) and the bearing housing (4).
 6. The turbocharger (1)as claimed in claim 5, wherein the cavity (6) is provided in an outercover region (7) as viewed in the radial direction (R) of the bearinghousing cover (5).
 7. The turbocharger (1) as claimed in claim 1,wherein the bearing housing cover (5) is provided with a metal bush (10)in a cover bore (9) which holds piston rings (8).
 8. An engine drivenvehicle, including an internal combustion engine having an air inlet andan exhaust outlet, an exhaust manifold connected to the engine exhaustoutlet, and a turbocharger (1) in the flow of the exhaust manifold,wherein the turbocharger comprises: a turbine (2), a compressor (3)which has a diffuser, a bearing housing (4) which is arranged betweenand is connected to the turbine (2) and the compressor (3) and which hasa bearing housing cover (5), wherein the bearing housing cover (5) isformed from a material with a thermal conductivity of less than 5 W/mK.